Pneumatic tire having a component containing high trans styrene-butadiene rubber

ABSTRACT

The invention is directed to a pneumatic tire having at least one component comprising a vulcanizable rubber composition, wherein the vulcanizable rubber composition comprises, based on 100 parts by weight of elastomer (phr), from about 30 to 100 phr of high trans random SBR, and from about zero to about 70 phr of at least one additional elastomer, wherein the high trans random SBR comprises from about 3 to about 30 percent by weight of styrene.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending Ser. No.10/224,984, filed Aug. 21, 2002 now U.S. Pat. No. 6,758,251.

BACKGROUND OF THE INVENTION

It is highly desirable for tires to have good wet skid resistance, lowrolling resistance and good wear characteristics. It has traditionallybeen very difficult to improve a tire's wear characteristics withoutsacrificing its wet skid resistance and traction characteristics. Theseproperties depend, to a great extent, on the dynamic viscoelasticproperties of the rubbers utilized in making the tire.

In order to reduce the rolling resistance and to improve the treadwearcharacteristics of tires, rubbers having a high rebound havetraditionally been utilized in making tire tread rubber compounds. Onthe other hand, in order to increase the wet skid resistance of a tire,rubbers which undergo a large energy loss have generally been utilizedin the tire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instance,various mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubbery material for automobile tire treads.

U.S. Pat. No. 6,103,842 and U.S. application Ser. No. 10/124,006, nowU.S. Pat. No. 6,627,715, disclose processes and catalyst systems for thecopolymerization of 1,3-butadiene monomer and styrene monomer into astyrene-butadiene copolymer having a high trans-1,4-polybutadienecontent and having a random distribution of repeat units which arederived from styrene. It is also therein disclosed thatstyrene-butadiene rubber made utilizing the catalyst system andtechniques therein may be used in the preparation of tire tread rubbercompounds which exhibit improved wear characteristics. What is notdisclosed is that superior wear characteristics may be obtained using alow styrene content in the high trans random SBR.

SUMMARY OF THE INVENTION

The current invention is directed to a pneumatic tire having at leastone component comprising a high trans solution styrene-butadiene rubber(HTSBR) with a random distribution of repeat units which are derivedfrom styrene. The invention is based on the highly surprising andunexpected discovery that a desirable balance of properties may berealized by using a HTSBR with a low styrene content.

It is then an object of the present invention to provide a pneumatictire having at least one component comprising a vulcanizable rubbercomposition, wherein the vulcanizable rubber composition comprises,based on 100 parts by weight of elastomer (phr), from about 30 to 100phr of high trans random SBR, and from about zero to about 70 phr of atleast one additional elastomer, wherein the high trans random SBRcomprises from about 3 to about 30 percent by weight of styrene.

DESCRIPTION OF THE INVENTION

The pneumatic tire of the present invention has at least one componentcomprising a high trans solution styrene-butadiene rubber HTSBR. ByHTSBR, it is meant an SBR produced by a solution method and having apercentage of trans-1,4-butadiene conformation in the polybutadienesegments of the polymer of greater than 60 percent by weight.Alternatively, suitable HTSBR may have a percentage oftrans-1,4-butadiene conformation in the polybutadiene segments of thepolymer of greater than 70 percent by weight. Suitable HTSBR may containfrom about 3 to about 30 percent by weight of styrene. Alternatively,suitable HTSBR may contain from about 3 to about 20 percent by weight ofstyrene. Alternatively, suitable HTSBR may contain from about 3 to about10 percent by weight of styrene.

Suitable HTSBR may be made by any of the suitable solutionpolymerization methods as are known in the art. In one embodiment,suitable HTSBR may be made using the methods of U.S. Pat. No. 6,103,842.In another embodiment, suitable HTSBR may be made using the methods ofU.S. application Ser. No. 10/124,006, now U.S. Pat. No. 6,627,715.Styrene-butadiene rubbers so made may contain from about 2 weightpercent to about 50 weight percent styrene and from about 50 weightpercent to about 98 weight percent 1,3-butadiene. However, in somecases, the amount of styrene included will be as low as about 1 weightpercent. In one embodiment of the present invention, suitablestyrene-butadiene rubber so made will contain from about 3 weightpercent to about 30 weight percent styrene and from about 70 weightpercent to about 97 weight percent 1,3-butadiene. In another embodiment,suitable styrene-butadiene rubber will contain from about 3 weightpercent to about 20 weight percent styrene and from about 80 weightpercent to about 97 weight percent 1,3-butadiene. In another embodiment,suitable styrene-butadiene rubber will contain from about 3 weightpercent to about 10 weight percent styrene and from about 90 weightpercent to about 97 weight percent 1,3-butadiene. Thesestyrene-butadiene rubbers typically have a melting point which is withinthe range of about below 44° C. Higher styrene content HTSBR may exhibitno melting point.

The styrene-butadiene rubber will typically have a glass transitiontemperature in a range of from about −55° C. to about −85° C.;alternatively from about −65° C. to about −85° C.

In suitable styrene-butadiene rubbers containing less than about 30weight percent bound styrene, the distribution of repeat units derivedfrom styrene and butadiene is essentially random. The term “random” asused herein means that less than 10 percent of the total quantity ofrepeat units derived from styrene are in blocks containing more thanfive styrene repeat units. In other words, more than 90 percent of therepeat units derived from styrene are in blocks containing five or fewerrepeat units. About 20% of the repeat units derived from styrene will bein blocks containing only one styrene repeat unit. Such blockscontaining one styrene repeat unit are bound on both sides by repeatunits which are derived from 1,3-butadiene.

In suitable styrene-butadiene rubbers containing less than about 20weight percent bound styrene, less than 4 percent of the total quantityof repeat units derived from styrene are in blocks containing five ormore styrene repeat units. In other words, more than 96 percent of therepeat units derived from styrene are in blocks containing less thanfive repeat units. In such styrene-butadiene rubbers, over 25 percent ofrepeat units derived from styrene will be in blocks containing only onestyrene repeat unit, over 60 percent of the repeat units derived fromstyrene will be in blocks containing less than 3 repeat units and over90 percent of the repeat units derived from styrene will be in blockscontaining 4 or fewer repeat units.

In suitable styrene-butadiene rubbers containing less than about 10weight percent bound styrene, less than 1 percent of the total quantityof repeat units derived from styrene are in blocks containing 5 or morestyrene repeat units. In other words, more than 99 percent of the repeatunits derived from styrene are in blocks containing 4 or less repeatunits. In such styrene-butadiene rubbers, at least about 50 percent ofrepeat units derived from styrene will be in blocks containing only onestyrene repeat unit and over about 85 percent of the repeat unitsderived from styrene will be in blocks containing less than 3 repeatunits.

Suitable styrene-butadiene copolymers also have a consistent compositionthroughout their polymer chains. In other words, the styrene content ofthe polymer will be the same from the beginning to the end of thepolymer chain. No segments of at least 100 repeat units within thepolymer will have a styrene content which differs from the total styrenecontent of the polymer by more than 10 percent. Such styrene-butadienecopolymers will typically contain no segments having a length of atleast 100 repeat units which have a styrene content which differs fromthe total styrene content of the polymer by more than about 5 percent.

In the broadest embodiment, suitable HTSBR may be made by any of thesuitable solution polymerization methods as are known in the art. In oneembodiment, suitable HTSBR may be produced using a process as taught inU.S. application Ser. No. 10/124,006, now U.S. Pat. No. 6,627,715, fullyincorporated herein by reference, that comprises copolymerizing styreneand 1,3-butadiene in an organic solvent in the presence of a catalystsystem that is comprised of

(A) an organolithium compound,

(B) a group IIa metal salt selected from the group consisting of groupIIa metal salts of amino glycols and group IIa metal salts of glycolethers, and

(C) an organometallic compound selected from the group consisting oforganoaluminum compounds and organomagnesium compounds.

In another embodiment, suitable HTSBR may be produced using a process astaught in U.S. Pat. No. 6,103,842, fully incorporated herein byreference, that comprises copolymerizing styrene and 1,3-butadiene underisothermal conditions in an organic solvent in the presence of acatalyst system which consists essentially of

(A) an organolithium compound,

(B) a barium alkoxide and

(C) a lithium alkoxide.

In one embodiment, the pneumatic tire of the present invention mayinclude a component comprising between about 30 and about 100 parts byweight of HTSBR. The component may also include between zero and up to70 parts by weight of other elastomers as are known in the art, to makeup a total 100 parts by weight of elastomer. In another embodiment, thepneumatic tire of the present invention may include a componentcomprising between about 50 and about 100 parts by weight of HTSBR. Thecomponent may also include between zero and up to 50 parts by weight ofother elastomers as are known in the art, to make up a total 100 partsby weight of elastomer.

Other elastomers that may be used along with the HTSBR may includevarious general purpose elastomers as are known in the art. The phrase“rubber or elastomer containing olefinic unsaturation” is intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition”, “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include a carboxylated rubber, silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polybutadiene, SBR, and natural rubber.

In one aspect the rubber to be combined with the HTSBR is preferably oneor more diene based rubbers. For example, one or more rubbers ispreferred such as cis 1,4-polyisoprene rubber (natural or synthetic,although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica), although precipitated silicas are preferred. Theconventional siliceous pigments preferably employed in this inventionare precipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas, preferably in therange of about 40 to about 600, and more usually in a range of about 50to about 300 square meters per gram. The BET method of measuring surfacearea is described in the Journal of the American Chemical Society,Volume 60, Page 304 (1930).

The conventional silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165 MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler.Representative examples of such carbon blacks include N110, N121, N220,N231, N234, N242, N293, N299, S315, N326, N330, M332, N339, N343, N347,N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762,N765, N774, N787, N907, N908, N990 and N991. These carbon blacks haveiodine absorptions ranging from 9 to 145 g/kg and DBP number rangingfrom 34 to 150 cm³/100 g.

It may be preferred to have the rubber composition for use in the tirecomponent to additionally contain a conventional sulfur containingorganosilicon compound. Examples of suitable sulfur containingorganosilicon compounds are of the formula:Z-Alk-S_(n)-Alk-Z  Iin which Z is selected from the group consisting of

where R⁶ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R⁷ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

Specific examples of sulfur containing organosilicon compounds which maybe used in accordance with the present invention include:3,3′-bis(trimethoxysilylpropyl)disulfide,3,3′-bis(triethoxysilylpropyl)disulfide,3,3′-bis(triethoxysilylpropyl)tetrasulfide,3,3′-bis(triethoxysilylpropyl)octasulfide,3,3′-bis(trimethoxysilylpropyl)tetrasulfide,2,2′-bis(triethoxysilylethyl)tetrasulfide,3,3′-bis(trimethoxysilylpropyl)trisulfide,3,3′-bis(triethoxysilylpropyl)trisulfide,3,3′-bis(tributoxysilylpropyl)disulfide,3,3′-bis(trimethoxysilylpropyl)hexasulfide,3,3′-bis(trimethoxysilylpropyl)octasulfide,3,3′-bis(trioctoxysilylpropyl)tetrasulfide,3,3′-bis(trihexoxysilylpropyl)disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl)trisulfide,3,3′-bis(triisooctoxysilylpropyl)tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl)disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl)tetrasulfide, 2,2′-bis(tripropoxysilylethyl)pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl)tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl)trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl)tetrasulfide,bis(trimethoxysilylmethyl)tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl)disulfide, 2,2′-bis(dimethylsec.butoxysilylethyl)trisulfide, 3,3′-bis(methylbutylethoxysilylpropyl)tetrasulfide, 3,3′-bis(dit-butylmethoxysilylpropyl)tetrasulfide, 2,2′-bis(phenyl methylmethoxysilylethyl)trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl)tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl)disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl)tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl)trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl)tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl)tetrasulfide, 3,3′-bis(ethyl di-sec.butoxysilylpropyl)disulfide, 3,3′-bis(propyldiethoxysilylpropyl)disulfide, 3,3′-bis(butyldimethoxysilylpropyl)trisulfide, 3,3′-bis(phenyldimethoxysilylpropyl)tetrasulfide, 3-phenyl ethoxybutoxysilyl3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl)tetrasulfide,6,6′-bis(triethoxysilylhexyl)tetrasulfide, 12,12′-bis(triisopropoxysilyldodecyl)disulfide, 18,18′-bis(trimethoxysilyloctadecyl)tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl)tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl)tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene)tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl)trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.

The preferred sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl)sulfides. The mostpreferred compounds are 3,3′-bis(triethoxysilylpropyl)disulfide and3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore as to formula I,preferably Z is

where R⁷ is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms beingparticularly preferred; alk is a divalent hydrocarbon of 2 to 4 carbonatoms with 3 carbon atoms being particularly preferred; and n is aninteger of from 2 to 5 with 2 and 4 being particularly preferred.

The amount of the sulfur containing organosilicon compound of formula Iin a rubber composition will vary depending on the level of otheradditives that are used. Generally speaking, the amount of the compoundof formula I will range from 0.5 to 20 phr. Preferably, the amount willrange from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. Preferably, the sulfur-vulcanizing agent iselemental sulfur. The sulfur-vulcanizing agent may be used in an amountranging from 0.5 to 8 phr, with a range of from 1.5 to 6 phr beingpreferred. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Such processing aidscan include, for example, aromatic, naphthenic, and/or paraffinicprocessing oils. Typical amounts of antioxidants comprise about 1 toabout 5 phr. Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others, such as, for example, thosedisclosed in the Vanderbilt Rubber Handbook (1978), Pages 344 through346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typicalamounts of fatty acids, if used, which can include stearic acid compriseabout 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2to about 5 phr. Typical amounts of waxes comprise about 1 to about 5phr. Often microcrystalline waxes are used. Typical amounts of peptizerscomprise about 0.1 to about 1 phr. Typical peptizers may be, forexample, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, preferably about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. Preferably, the primary accelerator is asulfenamide. If a second accelerator is used, the secondary acceleratoris preferably a guanidine, dithiocarbamate or thiuram compound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example theingredients are typically mixed in at least two stages, namely at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

Pneumatic tires are conventionally comprised of a generally toroidalshaped casing with an outer circumferential tread adapted to the groundcontacting space beads and sidewalls extending radially from andconnecting the tread to the beads. The rubber composition may beincorporated in a variety of rubber components of the tire. For example,the rubber component may be a tread (including tread cap and treadbase), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner.Preferably, the compound is a tread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire and the like. Earthmover and off-the-road tires may alsogenerally be referred to as industrial tires. In one embodiment, thetire is a passenger or truck tire. The tire may also be a radial orbias, with a radial being preferred.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. Preferably, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

In one embodiment, the pneumatic tire is an agricultural or industrialtire comprising a casing and a rubber tread disposed radially outwardlyof the casing, the tread having an inner tread and a plurality of treadlugs projecting radially from the inner tread, the tread comprising avulcanizable rubber composition comprising, based on 100 parts by weightof elastomer (phr),

(A) from about 30 to 100 phr of high trans random SBR comprising fromabout 3 to about 30 percent by weight of styrene; and

(B) from about zero to about 70 phr of at least one additionalelastomer.

In the case of a agricultural or industrial tire, the typical cure cyclefor curing a green tire utilizes high temperatures and longer cure timesthan is typical for smaller, passenger type tires. The longer cure timesand higher temperatures of cure are sufficient to cure the thick, heavyrubber components of the agricultural or industrial tire. Thesecomponents include the tread lugs which typically cure more slowly thatthe thinner parts of the tire. The tread lugs may have a width andlength in a range of from about 0.8 to about 2.75 inches, and a heightin a range of from about 1 to about 4 inches. The tread may further havea net-to-gross ratio in a range of from about 15 to about 40 percent asmeasured around the entire 360° circumference of a normally inflated andnormally loaded tire contacting a flat hard surface, as describedfurther hereinafter. As is known in the art, “Net-to-gross Ratio” meansthe ratio of the surface are of the normally loaded and normallyinflated tire tread rubber that makes contact with a hard flat surface,divided by the total area of the tread, including non-contactingportions such as grooves as measured around the entire circumference ofthe tire. Alternatively, the net-to-gross ratio may be in a range offrom about 15 to about 30 percent. Thus, the cure cycle of hightemperature and long time would be understood by one skilled in the artas characteristic of cure in an agricultural or industrial tire havingthick, heavy tread lugs.

In one embodiment, the agricultural or industrial tire may be cured at atemperature ranging from about 160° C. to about 190° C. In anotherembodiment, the agricultural tire may be cured at a temperature rangingfrom about 160° C. to about 180° C. The agricultural tire may be curedfor a time ranging from about 40 minutes to about 150 minutes. Inanother embodiment, the agricultural tire may be cured for a timeranging from about 60 minutes to about 120 minutes. Generally, the curetime and temperature is sufficient to cure the characteristically thick,heavy tread of the agricultural or industrial tire. The agricultural orindustrial tire having thick, heavy tread is characteristically curedusing the long times and high temperatures.

The following examples are presented for the purposes of illustratingand not limiting the present invention. All parts are parts by weightunless specifically identified otherwise.

EXAMPLE I

In this example, a series of high trans random solution SBR (HTSBR)polymers prepared following the teachings of U.S. application Ser. No.10/124,006, now U.S. Pat. No. 6,627,715, were compounded and tested forvarious physical properties. These polymers are characterized asindicated in Table 1.

The polymers were compounded with 60 phr of HTSBR and 40 phr of naturalrubber (NR), and with standard amounts of conventional curatives andprocessing aids as indicated in Table 2, and cured with a standard curecycle. Cured samples were evaluated for various physical propertiesfollowing standard tests protocols as indicated in Table 3.

TABLE 1 Sample 1 2 3 4 5 6 7 8 Styrene (%) 3.7 5.8 8.3 10.6 12.9 21.527.4 37.9 Trans 1,4 77.2 75 74.5 73 69.7 64.2 59.6 50.8 PBD (%) Cis 1,4-14.7 15 13.3 13.3 13.3 11.2 10.3 8.8 PBD (%) 1,2 PBD (%) 4.4 4.2 3.9 3.14.1 3.1 2.7 2.5 T_(g) −81.4 −79.8 −76.8 −77 −77 −66.2 −58 −49 T_(m) 1312 12 18 3 −3 — —

TABLE 2 Standard Compound Recipe Natural Rubber 40 HTSBR 60 Zinc Oxide 5Process Oil 12.5 Stearic Acid 2.5 Wax 1.5 Carbon Black 50 Sulfur 1.50Antidegradants¹ 2.75 Accelerators² 1 ¹p-phenylenediamine type²sulfenamide type

TABLE 3 Sample 1 2 3 4 5 6 7 8 Peel Strength, N Peel at 23° C. 366.7345.2 373.9 285.1 146.4 202.8 111.1 82.9 Peel at 95° C. 137.5 242.6 216214.8 57.8 88 151.2 76.2 Stress-Strain Modulus 300% (MPa) 3.72 5.93 3.495.56 3.4 3.44 5 3.7 Tensile (MPa) 17.5 22.2 19.8 23.4 17.7 18.1 20.416.8 Elongation (%) 749 644 784 644 792 757 693 725 Zwick Rebound 23° C.42.4 44.4 41.8 46 37.2 37.6 34.2 27.8 100° C. 50.4 55.2 50.8 57.8 45.247.2 46.4 41.8 DIN Abrasion Loss 68 63 67 71 74 82 97 119 (gm/cc)

EXAMPLE II

In this example, a trans solution SBR (HTSBR) polymer prepared followingthe teachings of U.S. application Ser. No. 10/124,006, now U.S. Pat. No.6,627,715, were compounded and tested for various physical properties,and compared with a commercially available emulsion SBR (ESBR).

The polymers were compounded at 100 phr of the polymer with standardamounts of conventional curatives and processing aids as indicated inTable 4, and cured using a standard cure cycle. Cured samples wereevaluated for various physical properties following standard testprotocols as indicated in Table 5.

TABLE 4 Compound Recipe (Parts by Weight) Sample 9 10 Trans SBR³ 100 0Emulsion SBR⁴ 0 100 Carbon Black 50 50 Processing Oil 12.5 12.5Antidegradants¹ 0.75 0.75 Stearic Acid 2.5 2.5 Zinc Oxide 5 5 Sulfur 1.51.5 Accelerators² 0.9 0.9 ¹p-phenylenediamine type ²sulfenamide type³High Trans SSBR (75 percent trans-1,4 PBD, 14 percent cis-1,4 PBD, 3percent 1,2 PBD, 8 percent styrene) Tg of minus 80° C. ⁴Emulsion SBR (65percent trans-1,4 PBD, 11 percent cis-1,4 PBD, 16 percent 1,2 PBD, 8percent styrene) Tg of minus 75° C.

TABLE 5 Compound Physical Properties Sample 9 10 Stress-Strain TensileStrength (MPa) 14.2 10.3 Elongation at break (%) 513 421 300% modulus(MPa) 5.4 6.2 Zwick Rebound  23° C. (%) 48 43 100° C. (%) 52 50 PeelStrength @ 95° C., N 284 161 DIN Abrasion Loss 59 78 (gm/cc)

The samples demonstrate the unexpectedly superior tear, rebound, andabrasion properties obtained for the HTSBR samples. This is particularlysurprising, since generally improvements in tear strength are realizedonly with a compromise in rebound and abrasion, and vice versa. Further,the tear values for the lower styrene content are surprisingly high. Forexample, the tear (peel) strength values at 23° C. and 95° C. forSamples 1, 2, 3, and 4 having styrene contents in a range of about 3 toabout 11 percent are significantly higher than the tear values forSamples 6 through 8 having styrene contents of greater than 20 percent.In addition, the room temperature and 100° C. rebound values for thesamples having lower styrene contents are superior to those for thesamples with higher styrene contents. DIN abrasion for the low styrenecontent samples is also significantly greater than for the higherstyrene content samples.

EXAMPLE III

In this example, a trans solution SBR (HTSBR) polymer prepared followingthe teachings of U.S. application Ser. No. 10/124,006, now U.S. Pat. No.6,627,715, were compounded using a typical tread recipe for anagricultural or industrial tire and tested for various physicalproperties, and compared with a commercially available emulsion SBR(ESBR).

The polymers were compounded at 100 phr of the polymer with standardamounts of conventional curatives and processing aids as indicated inTable 6, and cured using a standard cure cycle. Cured samples wereevaluated for various physical properties following standard testprotocols as indicated in Table 7.

TABLE 6 Compound Recipe (Parts by Weight) Sample No. 11 12 E-SBR 85 0HTSBR 0 85 Natural Rubber 15 15 Carbon Black 65 65 Aromatic process oil19 16 Sulfur 1.65 1.90

TABLE 7 Compound Physical Properties Sample No. 11 12 Ring Tensile (ASTMD412), Cured 74 min at 160° C. 100% Modulus (MPa) 1.48 1.36 300% Modulus(MPa) 6.22 6.16 Modulus Ratio (300/100) 4.20 4.53 Break Str (MPa) 14.5113.59 % Elongation 578 529 Shore A Hardness (ASTM D2240), Cured 74 minat 160° C. Hardness @ RT 68.7 65.9 Hardness @ 100° C. 52.8 54.8 ZwickRebound (ASTM 1054), Cured 74 min at 160° C. Rebound @ RT 31.3 36.9Rebound @ 100° C. 40.1 40.8 Ring Tensile (ASTM D412), Cured 74 min at160° C., Aging: 3 days at 90° C. in Air 100% Modulus (MPa) 2.03 2.11300% Modulus (MPa) 8.59 10.37 Modulus Ratio (300/100) 4.23 4.91 BreakStr (MPa) 13.4 14.12 % Elongation 473 412 Shore A Hardness (ASTM D2240),Cured 74 min at 160° C., Aging: 3 days at 90° C. in Air Hardness @ RT72.5 71 Hardness @ 100° C. 57.4 60.6 Zwick Rebound (ASTM 1054), Cured 74min at 160° C., Aging: 3 days at 90° C. in Air Rebound @ RT 32.6 39.7Rebound @ 100° C. 42 45.1 RPA, 150° C. Cure Uncured G′ (15%, 100° C.,.83 Hz) 142 212 T′02 (min.) 1.44 1.41 T′25 (min.) 7.86 5.59 T′90 (min.)21.00 13.67 G′ (1%, 100 C., 1 Hz) 1732 1923 G′ (10%, 100 C., 1 Hz) 9391159 G′ (50%, 100 C., 1 Hz) 644 807 TanD (10%, 100 C., 1 Hz) 0.206 0.182RPA, 191° C. Cure Uncured G′ (15%, 100° C., .83 Hz) 146 218 T′02 (min.)1.68 1.57 T′25 (min.) 2.07 1.87 T′90 (min.) 3.26 2.55 G′ (1%, 100 C., 1Hz) 1642 1668 G′ (10%, 100 C., 1 Hz) 819 908 G′ (15%, 100 C., 1 Hz) 731817 G′ (50%, 100 C., 1 Hz) 495 552 TanD (10%, 100 C., 1 Hz) 0.256 0.257Instron Tear (ASTM D624), Cured 74 + 5 min at 160° C. Avg Load (N) 343399 Energy (N-cm) 5222 6078 Avg Peak Load (N) 350 447 SD of Energy BtwnLimits 0.51 3.33 (1 = knotty, 5 = smooth) 1 1 Instron Tear (ASTM D624),Cured 74 + 5 min at 160° C., Aging: 3 days at 90° C. in Air Avg. Load(N) 325 407 Energy (N-cm) 6648 8330 Avg. Peak Load (N) 343 449 SD ofEnergy Btwn Limits 0.61 9.22 (1 = knotty, 5 = smooth) 3 2 DIN Abrasion(ASTM D5963, 10 N force), Cured 74 min at 160° C. Rel. Volume Loss (g)126 76 Room Temp Peel Strength, To Self, Cured 74 min at 160° C.SS-AVG.-LOAD (N) 154.45 161.61 (1 = knotty, 5 = smooth) 5 3 RT PeelStrength, To Self, Cured 74 min at 160° C., Aging: 3 days at 90° C. inAir SS-AVG-LOAD (N) 121.64 127.32 (1 = knotty, 5 = smooth) 5 3Rheometer, ODR, 150° C. Max Torque (dNm) 28.28 35.16 Min Torque (dNm)5.96 9.39 TS1 (min) 6.18 4.14 T25 (min) 9.59 6.38 T90 (min) 24.46 13.35Delta Torque (dNm) 22.32 25.77 tR2 71.12 Final Torque 27.83 31.94 Rev =(Max − Final) 0.45 3.22 Reversion Rate (dNm/120′) = Rev/ 0.57 3.62 (120− T90) * 120

Modern agricultural or industrial tire utilization requires a coolrunning tread, despite the extremely thick lug design, to enableextended running periods over paved roads at maximum speed, which isabout 30 kilometers per hour, four times the normal speed in the field.Use of the HTSBR polymer in agricultural and industrial treads willprovide reduced running temperature over the road with equivalentresistance to stubble and damage resistance in the field. The data oftables 6 and 7 show equivalent tear strength, better abrasionresistance, and better rebound compared to an emulsion SBR. The curestate can be altered to achieve an improvement in tear strength, yetequivalent abrasion and rebound.

The composition is especially useful for a radial rear farm tire tread,especially on the new high horse-power tractors, where cool runningtemperature is needed over the road in addition to superior resistanceto stubble damage in the field.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

1. An agricultural or industrial tire comprising a casing and a rubbertread disposed radially outwardly of the casing, the tread having aninner tread and a plurality of tread lugs projecting radially from theinner tread, the tread comprising a vulcanizable rubber compositioncomprising, based on 100 parts by weight of elastomer (phr), (A) fromabout 30 to 100 phr of high trans random SBR comprising from about 3 toabout 30 percent by weight of styrene and a trans 1,4 butadiene contentin the polybutadiene segments of the SBR of greater than 60 percent byweight, wherein said high trans random SBR is produced by a process thatcomprises copolymerizing styrene and 1,3-butadiene in an organic solventin the presence of a catalyst system that is comprised of (i) anorganolithium compound, (ii) a group IIa metal salt selected from thegroup consisting of group IIa metal salts of amino glycols and group IIametal salts of glycol ethers, and (iii) an organometallic compoundselected from the group consisting of organoaluminum compounds andorganomagnesium compounds; and (B) from about zero to about 70 phr of atleast one additional elastomer.
 2. The agricultural or industrial tireof claim 1, wherein said vulcanizable rubber composition comprises fromabout 50 to about 100 phr of high trans random SBR comprising from about3 to about 30 percent by weight of styrene, and from about 10 to about50 phr of at least one additional elastomer.
 3. The agricultural orindustrial tire of claim 1, wherein said high trans random SBR comprisesfrom about 3 to about 20 percent by weight of styrene.
 4. Theagricultural or industrial tire of claim 1, wherein said high transrandom SBR comprises from about 3 to about 10 percent by weight ofstyrene.
 5. The agricultural or industrial tire of claim 1, wherein saidhigh trans random SBR has a trans content of greater than 70 percent byweight.
 6. The agricultural or industrial tire of claim 1, wherein saidhigh trans random SBR has a glass transition temperature in a range offrom about −55° C. to about −85° C.
 7. The agricultural or industrialtire of claim 1, wherein said component is selected from the groupconsisting of tread cap, tread base, sidewall, apex, chafer, sidewallinsert, wirecoat and innerliner.
 8. The agricultural or industrial tireof claim 1, wherein said component is a tread cap or tread base.
 9. Theagricultural or industrial tire of claim 1, wherein said at least oneadditional elastomer is selected from the group consisting of cis1,4-polyisoprene rubber (natural or synthetic, although natural ispreferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber,styrene/isoprene rubber, emulsion and solution polymerization derivedstyrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsionpolymerization prepared butadiene/acrylonitrile copolymers.
 10. Theagricultural or industrial tire of claim 1, wherein said at least oneadditional elastomer is natural rubber.
 11. The agricultural orindustrial tire of claim 1, wherein said vulcanizable rubber compositionfurther comprises from about 20 to about 100 phr of carbon black. 12.The agricultural or industrial tire of claim 1, wherein saidvulcanizable rubber composition further comprises from about 20 to about100 phr of silica.
 13. The agricultural or industrial tire of claim 1,wherein less than 10 percent of the total quantity of repeat unitsderived from styrene in said high trans random SBR are in blockscontaining more than five styrene repeat units.
 14. The agricultural orindustrial tire of claim 1, wherein less than 4 percent of the totalquantity of repeat units derived from styrene in said high trans randomSBR are in blocks containing 5 or more styrene repeat units.
 15. Theagricultural or industrial tire of claim 1, wherein less than 1 percentof the total quantity of repeat units derived from styrene in said hightrans random SBR are in blocks containing 5 or more styrene repeatunits.
 16. The agricultural or industrial tire of claim 1, wherein saidhigh trans random SBR is produced by a process that comprisescopolymerizing styrene and 1,3-butadiene in an organic solvent in of acatalyst system that is comprised of (A) an organolithium compound, (B)a group IIa metal salt of an amino glycol, and (C) an organometalliccompound selected from the group consisting of organoaluminum compoundscontaining less than 13 carbon atoms and organomagnesium compounds. 17.The agricultural or industrial tire of claim 1, wherein each lug has awidth and length in a range of from about 0.8 to about 2.75 inches, anda height in a range of from about 1 to about 4 inches, and wherein thetread has a net-to-gross ratio in a range of from about 15 to about 40percent as measured around the entire 360° circumference of a normallyinflated and normally loaded tire contacting a flat hard surface. 18.The agricultural or industrial tire of claim 1, wherein said lugscomprise said composition.